Thread: speed-o help please

Tweet

If you want the true diameter of a tire, use a cloth or fiberglass tape to find the circumference of the tire, then divide by 3.14159. The circumference is what the roadway sees, not the loaded diameter.

Use a little math to find the proper speedo gears for your TH350.....
http://www.tciauto.com/tc/speedomete...alculator/#350

Originally Posted by techinspector1

If you want the true diameter of a tire, use a cloth or fiberglass tape to find the circumference of the tire, then divide by 3.14159. The circumference is what the roadway sees, not the loaded diameter.

Use a little math to find the proper speedo gears for your TH350.....
Speedometer Gear Calculator and Charts - TCI® Auto

I agree, Tech. Inflation pressure (and the size of the flat spot) doesn't affect tire speed. You want the actual tire diameter, and your approach of measured circumference divided by pi is more accurate than trying to measure the diameter.